NMR Evidence of Weak Continuous Transitions in Water and Aqueous Electrolyte Solutions

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Nuclear magnetic resonance chemical shifts are used to examine the perturbations in water structure that occur with concentration changes in aqueous KF, KCl, and LiOH solutions. Changes in the slope of ion chemical shifts as a function of solute concentration can be explained by changes in water structure. The equilibrium shift in water structure occurs as a result of changes in the hydrogen bond strength. The changes in hydrogen bond strength are a result of changes in electrolyte concentration and electron delocalization throughout the liquid. The location of the changes in slope with concentration is temperature dependent. A correlation of the changes in slope of chemical shifts to minima in specific heat capacity suggests the occurrence of a weak continuous transition in the solution structure at the critical concentration corresponding to the specific heat capacity minimum. By extrapolation the experiments reported here imply that there is a weak continuous transition associated with the heat capacity minimum for pure water. There must also be a structural relaxation time in the liquid associated with this transition. The results of these experiments provide confirmation for the model of aqueous solutions we recently proposed in which the solution is composed of regions of pure water and regions of liquid crystalline electrolyte hydrates. The subphase composed of structurally perturbed water is the part of the system that participates in the weak continuous phase transition that is evidenced by the NMR chemical shifts. In complete agreement with earlier Raman experiments it appears that the entire solution is a single electronic whole with exquisite electronic delocalization between the water and liquid crystalline subphases so that the ionic nuclei experience the electronic effects of the transition in the water subphase.